Ah, my trusty DS Lite. Blue/Black. Faithful companion for those dreary Phases of Matter lectures (Chemistry, in my Physics degree? It's more likely than you'd think.), and any other time I can't be bothered working/sleeping.

A black DSi. BTW, do white consoles finally get black or gray because of dirt? I'm SO obsessive about dirt that I use to wash my hands BEFORE I touch my DSi. So, I have a black DSi protected with a black cover (brand: Thrustmaster, something between metal and plastic).

I started with the classic grey DS phat, imported from Japan.
Then I got a white DS Lite, also imported from Japan. Around that time I sold off my old DS phat.
Eventually, that system got worn down, my old R4 would freeze often, the buttons getting unresponsive, and for Christmas I got a Silver DS Lite, loved it.
Finally, I got a Black DSi at launch, totally worth it.

Probably won't get a DSi XL, it's a very nice system but it's not portable and my DSi is still doing great, it's nearly a year old now.

These days, I play on my DSi, whilst my Silver DS Lite is still used for GBA games or trading pokémon across games. My White DS Lite has a Supercard Lite, which I use for dumping roms, running pokémon distros, or just as a cooking timer.